Plug fuse



' Nov. 22, 1966 C. R. D. KINDERSLEY ETAL PLUG FUSE Filed Nov. 12, 1964 2 Sheets-Sheet 1 Nov. 22, 1 6 c. R. Di KINDERSLEY ETAL 3,287,529

PLUG FUSE Filed Nov. 12, 1964 i 2 Sheets- 5mm: 2

United States Patent 3,287,529 PLUG FUSE Charles Richard Dirom Kindersley, deceased, late of Georgetown, Ontario, Canada, by The Royal Trust Company, administrator, Toronto, Ontario, Canada, and Joseph F. Dutlield, Georgetown, Ontario, and John Richard Glynn, Limehouse, Ontario, Canada, assignors to Smith & Stone Limited, Toronto, Ontario, Canada, a company of Ontario Filed Nov. 12, 1964, Ser. No. 410,809 12 Claims. (Cl. 200-130) This invention relates to electrical plug fuses of the plastic body and metal shell contact type. Prior known plug fuses have been manufactured by assembling metallic and insulating elements together, including a fusing strip or link which electrically connected the two poles of the fuse together. Various attempts to reduce the number of components or cost of manufacture have resulted in plug fuses which in some cases are unacceptable from the safety point-of-view, and which fail to pass the acceptance tests laid down by standards authorities.

One of the problems known to exist with prior plug fuses has been the dissipation of gases produced when the fuse burns. Where a path for the hot gases has been provided, the gas produced has in many cases impinged on the female contact which receives the plug fuse causing possible adhesion of the fuse to the female contact.

It is a feature of this invention to provide a plug fuse having a minimum number of parts, said parts requiring substantially less material than known plug fuses.

It is a further feature of this invention to provide a plug fuse having a reduced amount of moulding material while having increased strength and rigidity.

It is a further feature of this invention to provide a plug fuse which may be assembled with a minimum number of operations.

It is another feature of this invention to provide a plug fuse which includes as large an internal air space as possible and means whereby hot gases produced during fusing may escape without damaging associated panel equipment.

By a broad aspect of the invention, there is provided an electric plug fuse of the shell contact type having gas escape means, comprising an insulated body member having a shell contact supporting portion radially inwardly spaced from said shell contact, said space extending substantialy the entire length of said contact, a centre contact, and means restricting the escape of fusing gases to a substantially non-radial direction from the centre contact end of said fuse.

A preferred embodiment of the invention is now described with reference to the accompanying drawings in which:

FIG. 1 is an exploded isometric view of a plug fuse according to one aspect of the present invention;

FIG. 2 is a plan view of the base connection end of the plug fuse;

FIG. 3 is a vertical sectional elevation of part of the plug fuse taken along the lines 33 of FIG. 2 with the contacts and fuse assembled therein and,

FIG. 4 is a plan view of the window end of the plug fuse shown in FIGS. 2 and 3.

FIG. 5 is similar .to FIG. 3 and shows an alternative fusing element in the form of a ribbon.

FIG. 6 is a plan view of the base connection end of the plug fuse shown in FIG. 5.

FIG. 7 is an enlarged sectional detail of part of the assembled plug fuse shown in FIG. 5;

FIG. 8 shows, to an enlarged scale, details of the centre contact of the plug fuse shown in FIG. 5;

FIG. 9 shows, details of the retainer for the centre con- 3,287,529 Patented Nov. 22, 1966 tact shown in FIG. 7, to the same scale as in FIG. 8, and

FIG. 10 is an inverted isometric view of the shell contact shown in FIG. 5 at one stage of manufacture.

Referring to FIGS. 1 and 3, there is shown a base generally indicated at 1. The base includes a hollow cylindrical portion 2 in which is incorporated a counterbore 3 provided with radial ribs 4, counterbore 3 receiving and retaining a window to be described, hereinafter.

The ribs 4 serve to restrict the movement of the window or closure 30. The inner surface of portion 2 adjacent the upper end has a radius 2a, provided to facilitate the fitting of a closure 30. The portion 2 includes a shoulder 5, of reduced diameter, for axially locating a screwshell contact 26 to be described hereinafter. Coaxially disposed and integrally formed with the portion 2 is a hollow conical portion 6, truncated by a base end wall 7.

The end Wall 7 includes a longitudinal slit 8 and a dimple 9. Projecting radially outwardly from the outer surface of the conical portion 6 are three segments 10, best seen in FIGS. 2 and 3, the segments having thread formations 11 on the outer cylindrical surfaces thereof. The thread formations 11 on the three segments are defined by parts of a common helix. At the lower end of each segment 10 there is included a longitudinally inset recess 10a, shown in FIGS. 2 and 3.

Immediately above each of the three segments 10 are rectangular vent apertures 12 radially disposed in the walls of the hollow conical portion 6, the apertures extending upwardly substantially to the plane of the junction between the portion 2 and the conical portion 6, thereby further defining a longitudinal gap 12a, best seen in FIG. 3.

Within each vent aperture 12 there is provided a pair of longitudinally disposed circumferentially oriented ribs 13 as best seen in FIGS. 1 and 4, the lower end of each rib being formed integrally with the segments 10. Within the hollow conical portion 6, at the base end thereof, there is included a single substantially radial rib 14 which includes a side 15 which slopes downwardly to meet the longitudinal slit 8. Diametrically opposite the rib 14 and one of said apertures 12, there is provided, an additional longitudinal radial rib 16, projecting inwardly from the inner conical surface of the portion 6.

The base may be formed by pressure moulding from any suitable thermoplastic material.

FIG. 1 also shows the contact and fuse link assembly generally indicated at 17. The contact fuse link assembly 17 comprises a top portion 18, a side portion 19, a bottom portion 20, an intermediate portion 21. The top portion 18 includes an offset region 18a which provides a gap across which a fusing link 22 is subsequently spanned, which link is spot welded or otherwise electrically connected to the top portion 18. The offset region is severed after assembly as will be described hereinafter. The side portion 19 includes an outwardly directed dimple 23. The bottom portion 20 is provided with a tab 24, and the intermediate portion includes an aperture 25 therein. Apart from the fuse link 22, the contact assembly may be made of any suitable contact material, for example, brass. The fuse 22 may be made of any suitable contact material appropriate to the fuse characteristics required, as for example, Zinc.

The screwshell, generally indicated at 26, in FIG. 1, comprises a hollow cylindrical portion 27, turned in at one end thereof, to form an apertured end wall 28. The cylindrical portion 27 has a thread formation 29 formed thereon. The screwshell may be formed in any suitable contact material for example, copper or brass.

FIG. 1 also indicates a window or closure 30, through which is necessary, the fuse per se may be viewed, if transparent material is used. The window or closure 30 is preferably formed in concavo-convexo configuration and may be made from any suitable slightly resilient plastic material.

The plug fuse is assembled as follows:

The contact and fuse assembly 17 is dropped into the open end base 1 so that the bottom portion 20 of the contact passes through the slit 8 in the end wall 7, and the side portion 23 simultaneously passing through one of the gaps 12a, leaving dimple 23 projecting radially outwards, thereby forming a side contact 23a. The rib 14 assists in guiding portion 20 of the contact into the slit 8 during the assembly operation. In the process of inserting the contact assembly 17 into the base, the aperture 25 in the intermediate portion 21 of the contact assembly is engaged with the rib 16 on the inner wall of the base 6. The bottom portion 20 is then bent inwardly to lay against the end wall 7 of the base, thereby to form a centre contact. To hold the bottom portion 20 in position, the tab 24 is bent inwardly into the dimple 9. After the contact assembly 17 is locked into position, the screwshell 26 is screwed upwardly, by engagement with the thread formations 11 on the segments 10, until the open end of the screwshell 26 abuts against the underside of the shoulder 5. In this position the screwshell 26 is placed in electrical contact with the dimple 23 on the side portion 19 of the contact assembly 17. To lock the screwshell 26 in this final position, at least one portion 28b of the apertured end wall 28 is forced into an associated recess a in the end of a segement 10 as seen in FIG. 3. The apertured end wall will be seen to provide a narrow annular passage 28a. The oifset region 1811 of the contact is then severed from the remaining portions of the contact and fuse link assembly 17, leaving the fuse link 22 electrically connected between side portion 19 and the intermediate portion 21. Finally, the closure 30 is forced into the groove 3 in the base 6, where it is retained therein by the inherent resilience of the material from which the closure is made. The ribs 4 assist in aligning the edge of closure 30 within the groove.

When the plug fuse is then assembled, it will be seen that any gases produced during burning of the fuse may pass through vent aperture 12 in the base 1, into the annulus formed between the outer conical surface of portion 6 and the screwshell 26. This annulus provides a buffer to the expanding gases produced by burning of the fuse. The gases are then free to escape, harmlessly, toward the fusepanel bus bars, by passing through the gap 28a (in FIG. 3) between the apertured end wall 28 of the screwshell 26, and the conical shaped portion 6 of the base 1.

The conical form of the body reduces the amount of moulding material required whilst at the same time increasing its mechanical strength and rigidity.

The above described preferred embodiment provides for many alternatives without departing from the scope of the invention.

The groove 3 is the base 1 may be omitted, in which case the ribs 4 therein, may include radial recesses to accommodate the closure 30.

The lower portion of the base 1 may be formed other than in hollow configurations which converge toward the base. It is only necessary that an annulus 28a is provided between the outer surface of the portion 6 and the screwshell 26, and that a path be provided for the escape of gases from the interior of the base of this annulus. The interior of portion 6 must of course, provide sufficient space for fitting the contact assembly 17 The number of segments 10 need not be limited to three. Any number more than two may be used, but preferably any odd number, since it is desirable that the aperture 12 through which the contact portion 19 is passed, is diametrically opposite a nonapertured part of the conical portion 6, in order that the rib 16 may preferably be included to assist in locating the contact assembly 17 The rib 14 serves to assist assembly but the plug fuse could be assembled with care in the absence of the rib. The means of locking the screwshell against unscrewing by forcing the portion 28b in end wall 28 into the recesses 10a is but one of several that would appear obvious to those skilled in the art.

Referring now to FIG. 5 there is shown a plug fuse similar to the plug fuse shown in FIG. 3 wherein the fuse link assembly 17 of that Figure is replaced by a single ribbon of fuse material 35. It will be seen that the ribbon 35 passes radially outwardly through the side of the base 6 through one of the radial apertures 12a and it is retained in this position by the shell contact 26 which is screwed on tightly against the reduced portion 5 of the base 6. The lower end 31 of the ribbon 35 passes out through longitudinal slit 8 in the end 7 of the base 6 where it is afterwards bent across the end and severed adjacent dimple 9.

FIGURE 7 shows the radial aperture 12a with the ribbon threaded therethrough prior to screwing home the shell. contact 26.

FIGURE 8 shows the lower end of the base 6 to a larger scale and further showing the ribbon 35 held in position by a retainer 32 shown best in FIGURE 9.

FIGURE 10 shows the shell of FIG. 1 at one stage during its manufacture. The shell is first formed with the thread formations 29 on the outer cylindrical surface and without the aperture in the end wall having being punched therefrom. The retainer 32 shown in FIGURE 9 is punched out of the material forming the end of the shell contact 26 and in FIGURE 10 the outline of the retainer is shown at 33. The retainer 32 thus stamped from the end is subsequently bent into configuration shown in FIGURE 9. The retainer 32 includes a base 34, an upturned tab 35, and an upturned extension 36. The extension 36 includes a pair of severances 37 which enable the extension 36 to be bent into a slightly bowed shape thereby to provide a pair of detents 38 which detents serve to ensure that the retainer 32 looks into the base 6. Subsequently, a circular aperture in punched out of the end wall of the shell contact 26 to form the final configuration shown in FIGURE 1. Not only does this enable several pressing operations to be accomplished at one time, but it also enables material otherwise waste-d to be utilized in the production of the retainer.

In this further embodiment the ribbon fuse 25 may be formed from zinc or other suitable fusing material and again the shell contact 26 and retainer 32 are formed from brass or copper or other suitable contact material. Once the ribbon 35 has been located at the bottom by the retainer 32 and at the top by the shell contact 26, the ribbon is clipped in order to provide a desired fuse rating for the plugs used. Once the fuse ribbon 35 has been clipped to the above-mentioned desired fuse rating the closure 30 is placed in position and the fuse is subject to a continuity test.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A plug fuse comprising: (1) a hollow base moulded in insulating material, said base including:

(a) an open end for receiving a contact assembly, and a closed end, said closed end having a first contact receiving aperture therein,

(b) closure receiving and retaining means adjacent said open end,

(c) shell contact locating means, adapted to space a concentrically disposed shell contact away from said body over a substantial length of said shell contact thereby providing an annulus,

(d) a first vent aperture in said base providing for substantially unrestricted passage of gas from the interior of said base into said annulus, and,

(e) a second contact receiving aperture in said base;

(2) a shell contact received by said shell contact receiving means, said shell including:

(a) a hollow cylindrical portion having thread engaging means on the outer surface thereof, and

(b) an inturned flange portion at one end of said cylindrical portion, defining at and with said closed end of said base, firstly, a longitudinal limit of said annulus, and secondly, a non-radial escape passage for gas flow from said annulus, the other end of said cylindrical portion forming with said base a substantially gas-tight joint,

(3) a fuse element comprising:

(a) a first portion including one end,

(b) an intermediate portion integrally attached to said first portion,

(c) a second portion including said other end, and

(d) a bridge portion initially integrally attached to said second and intermediate portions, said part of said fuse element being electrically connected to said intermediate and second portions, said bridge portion being adapted for severance from said second and intermediate portions thereby to provide a path for the passage of current between said intermediate and second portions; said one end being located in said first contact receiving aperture and retained therein by a first contact retaining means, said one end forming at least part of a center contact, the other end of said fuse element being located in said second contact receiving aperture and retained therein by said shell contact, said shell contact making an electrical connection with said other end, at least a part of fuse element comprising fusible metal; and

(4) a closure for reception in said base and retention therein by said closure retaining means.

2. The plug fuse of claim 1 wherein said closed end of said base includes a recess and wherein said contact retaining means comprises an inturned portion on said first portion of said element, said inturned portion being received in said recess.

3. The plug fuse of claim 1 wherein said second portion of said element includes an outwardly directed dimple, said dimple being adapted for electrical connection with the inner cylindrical surface of said shell contact.

4. The plug fuse of claim 1 wherein said base includes a rib on the inner surface thereof and said intermediate portion of said fuse element including an aperture therein, said aperture receiving rib.

5. The plug fuse of claim 1 wherein said closure comprises a transparent window.

6. The plug fuse of claim 5 wherein said window has concavo-convexo configuration.

7. The plug fuse of claim 5 wherein said window is formed in mouldable plastic.

8. The plug fuse of claim 1 wherein said base includes: (a) a hollow cylindrical portion adjacent said open end, and (b) a hollow frusto-conical portion including said closed end intergrally attached to said cylindrical portion. 9. A plug fuse comprising: (1) a hollow base moulded in insulating material,

said base including:

(a) an open end for receiving a contact assembly, and a closed end, said closed end having a first contact receiving aperture therein,

(b) closure receiving and retaining means adjacent said open end,

(c) shell contact locating means, adapted to space a concentrically disposed shell contact away from said body over a substantial length of said shell contact thereby providing an annulus,

(d) a first vent aperture in said base providing for substantially unrestricted passage of gas from the interior of said base into said annulus, and,

(e) a second contact receiving aperture in said base;

(2) a shell contact received by said shell contact receiving means, said shell including:

(a) a hollow cylindrical portion having thread engaging means on the outer surface thereof, and

(b) an inturned flange portion at one end of said cylindrical portion, defining at and with said closed end of said base, firstly, a longitudinal limit of said annulus, and second, a non-radial escape passage for gas flow from said annulus, the other end of said cylindrical portion forming with said base a substantially gas-tight joint;

(3) a fuse element comprising a ribbon of fusible metal and having one end located in said first contact receiving aperture and retained therein by a first contact retaining means, said one end forming at least part of a center contact, the other end of said fuse element being located in said second contact receiving aperture and retained therein by said shell contact, said shell contact making an electrical connection with said other end, said first contact retaining means comprising a metallic stamping including a center contact region and an extension, a detent on said extension, said extension being received in said first contact receiving means thereby maintaining electrical connection with said one end of said fuse element; and

(4) a closure for reception in said base and retention therein by said closure retaining means.

10. The plug fuse of claim 9 wherein said ribbon is clipped to provide a selected fuse rating.

11. A plug fuse comprising:

(i) a base moulded in insulating material, said base including:

(a) a hollow cylindrical portion having a counterbore therein adapted to receive and retain a circular window, and a shoulder formed adjacent one end thereof;

(b) a hollow frusto-conical portion closed at the smaller end thereof by an end wall, the larger end of said frusto-conical portion being integrally attached, the said shoulder end of said cylindrical portion, a longitudinally disposed aperture in said end wall adapted to receive a contact, and a recess in the outer surface of said end wall,

(c) three shell contact locating segments extending radially outwards from said frusto-conical portion, said segments having thread engaging means thereon adapted to receive and engage a threaded shell contact and to space said shell contact away from said base over a substantial length of said shell contact, thereby to provide an annulus, said segments having longitudinally disposed recesses therein adapted to cooperate with a shell contact to provide locking therefor,

(d) three radially disposed vent apertures in said frusto-conical portion and substantially aligned with said segments, at least one vent aperture being adapted to receive a contact,

(ii) a shell contact comprising:

(a) a hollow cylindrical portion having a thread formation on the respective inner and outer surfaces thereof,

(b) an end wall having an aperture therein, said shell contact being received on said shell contact locating segments, said end wall defining at and with the small end of said frusto-conical portion, firstly, a longitudinal limit of said annulus, and secondly, a non-radial escape passage for gas fiow from said annulus, and the other end of said cylindrical portion forming with said shoulder a substantially gas-tight joint,

(iii) a fuse element comprising,

(a) a first portion received in said aperture in the end wall of said base, said first portion being bent to form a centre contact region, a tab integrally attached to said first portion, said tab being bent into said recess,

(b) an intermediate portion integrally attached to said first portion,

() a second portion received in said aperture in said vent aperture,

(d) a side portion integrally attached to said second portion, said side portion forming a side con tact electrically connected to said shell contact,

(e) an oflset bridge portion forming said intermediate and second portions, said bridge portion being adapted for severance from said intermediate and second portions, and

(f) a fuse link electrically connected to said intermediate and second portions, said bridge portion being severed from said intermediate and second portions after such electrical connection; and, 7

(iv) a window of concavo-convexo configuration formed in transparent material, said window being received and retained in said counterbore in said base.

12. A plug fuse comprising:

(i) a base moulded in insulating material, said base including:

(a) a hollow cylindrical portion having a counterbore therein adapted to receive and retain a circular window, and a shoulder formed adjacent one end thereof,

(b) a hollow frusto-conical portion closed at the smaller end thereof 'by an end wall, the larger end of said frusto-conical portion being integrally disposed recesses therein adapted to cooperate with a shell contact to provide locking therefor,

(d) three radially disposed vent apertures in said frusto-conical portion and substantially aligned with said segments, at least one vent aperture being adapted to receive a contact,

(ii) a shell contact comprising:

(a) a hollow cylindrical portion having a thread formation on the respective inner and outer surfaces thereof,

(b) an end wall having an aperture therein, said shell contact being received on said shell contact locating segments, said end wall defining at and with the small end of said frusto-conical portion, firstly, a longitudinal limit of said annulus, and secondly, a non-radial escape passage for gas flow from said annulus, and the other end of said cylindrical portion forming with said shoulder a substantially gas-tight joint,

(iii) a fuse element comprising:

(a) a ribbon of fusible metal having a first end received in said vent aperture in said body, said first end being clamped against said body by said shell contact and maintained thereby in electrical connection with said shell contact, a second end received in said longitudinally disposed aperture in said end wall of said body, said second end being bent to form at least part of a centre contact,

(iv) a contact retainer comprising a metallic stamping including a centre contact region and an extension, a detent on said extension, said extension being received in said longitudinal aperture and in electrical contact with the said second end and retained in said longitudinal aperture by said detent means, and,

(v) a window of concavo-convexo configuration formed in transparent material, said window being received and retained in said counterbore in said base.

References Cited by the Examiner UNITED STATES PATENTS 1,001,694 8/1911 Sargent 200l30 1,277,647 9/1818 Schroenberg 200-- 1,581,637 4/1926 Jung 200-130 1,621,349 3/1927 Brown 200--130 1,968,642 7/1934 Gunthorp 20013O BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. A PLUG FUSE COMPRISING: (1) A HOLLOW BASE MOULDED IN INSULATING MATERIAL, SAID BASE INCLUDING: (A) AN OPEN END FOR RECEIVING A CONTACT ASSEMBLY, AND A CLOSED END, SAID CLOSED END HAVING A FIRST CONTACT RECEIVING APERTURE THEREIN, (B) CLOSURE RECEIVING AND RETAINING MEANS ADJACENT SAID OPEN END, (C) SHELL CONTACT LOCATING MEANS, ADAPTED TO SPACE A CONCENTRICALLY DISPOSED SHELL CONTACT AWAY FROM SAID BODY OVER A SUBSTANTIAL LENGTH OF SAID SHELL CONTACT THEREBY PROVIDING AN ANNULUS, (D) A FIRST VENT APERTURE IN SAID BASE PROVIDING FOR SUBSTANTIALLY UNRESTRICTED PASSAGE OF GAS FROM THE INTERIOR OF SAID BASE INTO SAID ANNULUS, AND, (E) A SECOND CONTACT RECEIVING APERTURE IN SAID BASE; (2) A SHELL CONTACT RECEIVED BY SAID SHELL CONTACT RECEIVING MEANS, SAID SHELL INCLUDING: (A) A HOLLOW CYLINDRICAL PORTION HAVING THREAD ENGAGING MEANS ON THE OUTER SURFACE THEREOF, AND (B) AN INTURNED FLANGE PORTION AT ONE END OF SAID CYLINDRICAL PORTION, DEFINING AT AND WITH SAID CLOSED END OF SAID BASE, FIRSTLY, A LONGUTIDUNAL LIMIT OF SAID ANNULUS, AND SECONDLY, A NON-RADIAL ESCAPE PASSAGE FOR GAS FLOW FROM SAID ANNULUS, THE OTHER END OF SAID CYLINDRICAL PORTION FORMING WITH SAID BASE A SUBSTANTIALLY GAS-TIGHT JOINT, 